Cow's milk allergy (CMA) is defined as an immune-mediated adverse reaction to cow's milk proteins. The present treatment of choice is the complete elimination of cow's milk antigens. In infants with CMA, it is necessary to use a substitute formula when human milk is unavailable. Hydrolysed formulae, based on cow's milk-derived whey or casein, are used to provide adequate nutrition with a reduced antigenic load. The preliminary heat treatment of cow's milk mainly affects the conformation of proteins and facilitates their hydrolysis. Subsequent enzymatic hydrolysis with pepsin, trypsin, pancreatic extracts and extracts from the intestinal mucosa causes progressive destruction of sequential epitopes and refines the formulae into the least antigenic and allergenic form.
In most cases, extensively hydrolysed cow's milk-derived formulae can be safely introduced and these are efficient and clinically and metabolically well tolerated. Enzymatic hydrolysis, however, does not necessarily make the formulae nonallergenic, as the optimal extent of hydrolysis is not known and traces of the original protein are detected in the hydrolysate. Therefore, introduction of these substitutes to children with cow's milk allergy must be cautious.
The approach to control allergic inflammation by antigen elimination has not been satisfactory, particularly in patients with multiple food allergies (Sampson et al., 1992). These patients frequently show increased intestinal permeability and dysfunction of the intestine's defence barrier (Majamaa et al., 1996, Majamaa and Isolauri, 1996). This enhances the risk for growth disorders and sensitization to multiple foods. New approaches are urgently needed for the treatment of cow's milk allergy to improve the substitute formulae in CMA.
Intestinal antigen handling determines subsequent immune response to the antigen. In health, antigens are absorbed across epithelium along two functional pathways. The main pathway is degradative reducing the immunogenicity of the antigen. A minor pathway allows the transport of intact proteins which is crucial for antigen-specific immune responses. Aberrant antigen absorption enhances the sensitization process (Fargeas et al., 1995).
Differential production of cytokines by T-helper (Th) cells during an immune reaction has important regulatory effects on the nature of the immune response. The cytokine profile of the natural immune response determines the phenotype of the subsequent specific immune response. Apart from controlling IgE synthesis, IL-4 is crucial for the development and maturation of the Th2 phenotype, characterized for allergic inflammation.
This process appears crucial for the development of tolerance to ingested protein. Oral tolerance is a state of antigen-specific systemic non-responsiveness characterized by local antigen-specific IgA response.
An isolated human intestinal strain, Lactobacillus strain GG (Lactobacillus GG, ATCC 53103) has recently been shown to promote local IgA responses against dietary antigens encountered by the enteric route and may therefore aid in immune elimination (Isolauri et al., 1993). It is not as yet known whether particular strains of intestinal bacteria could directly modify the immunogenicity of the food antigens and consequently downregulate hypersensitivity reactions.
Lactobacilli are included in the microbial flora of healthy intestines. It has been assumed that Lactobacilli act in the intestinal tract by competing for receptors and nutrients against pathogenic microbes on the intestinal mucosa.
Probiotics are viable microbial preparations which promote health by maintaining the natural microflora in the gut. A microbial preparation can be acknowledged as a probiotic if the functioning microbes thereof and their mode of action are known. The probiotics attach on the intestinal mucosa, colonize the human intestinal tract and prevent attachment of harmful microbes. A crucial presumption is that they get up to the gut's mucosa and do not get destroyed in the upper part of the gastrointestinal tract. Lactobacillus GG is one of known bacteria having probiotic characteristics.